Cosmic Alchemy: How Are We Made ?

1. Cosmic Alchemy: How Are We Made ? Prof. Paddy Regan FInstP Department of Physics University of Surrey Guildford, GU2 7XH p.regan@surrey.ac.uk

2. Medieval alchemist…trying to turn base metals into gold… Mistake…to try and use ‘chemistry’…needed nuclear physics

3. the neutron the nucleus radioactivity Marie Curie (see later) Nobel Physics 1903 Nobel Chemistry 1911 the electron Ernest Rutherford Nobel Chemistry 1909 Founder of Nuclear Physics For element X write AXN Z J J Thomson Nobel Physics 1906 Atoms comprise nuclei andelectrons - known since 1910 Nuclei comprise protons andneutrons - known since 1932 Z = number of protons N= number of neutrons A = N+Z = mass number neutral atom has Z electrons m(nucleon)  2000  m(electron)

4. Atoms (‘indivisible’) …… ~10-10 m, electrons (and their orbital structure) determine chemistry of the elements, e.g., NaCl Nuclei…..~10-14m across, protons determine the chemical element (Z); neutron number (N) determines the mass, (A = N+Z). > 99.9 % of the mass of the atom is in the nucleus. Nucleons (protons and neutrons ~10-15m) have a substructure, three quarks in each nucleon (‘ups’ and ‘downs’)…but they don’t exists on their own.

5. Mendeleyev

10. Moseley’s Law….evidence for Atomic numbers…. ‘Characteristic’ X-rays…with a chemical (Z) dependence

11. Z=43 Tc Z=61 Pm Z=84 Po Elemental composition of the Solar Nebula

12. Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page 33-38 Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209Bi...why?

13. X-rays come from atomic ‘vacancies’ i.e. holes in the electron shells around the atom. Quantum mechanics means that the electron orbits are fixed in energy…. X-rays come from an electron ‘dropping’ from one energy level to a lower one

14. X-rays come from atomic ‘vacancies’ i.e. holes in the electron shells around the atom. Quantum mechanics means that the electron orbits are fixed in energy…. X-rays come from an electron ‘dropping’ from one energy level to a lower one

15. X-rays come from atomic ‘vacancies’ i.e. holes in the electron shells around the atom. Quantum mechanics means that the electron orbits are fixed in energy…. X-rays come from an electron ‘dropping’ from one energy level to a lower one X-ray emitted

17. Spectral Maps of the Galaxy Ref http://adc.gsfc.nasa.gov/mw/mmw_images.html

18. Radioactive 26Al around the Galaxy…. Diehl et al., Astron. Astrophys 97, 181 (1993) Full-sky Comptel map of 1.8 MeV gamma rays in 26Mg following 26Al b-decay. Nuclear reactions are taking place continually around the galaxy.

19. Chart of the Nuclei 6 5 4 Z = No. of Protons 3 2 11B 12C 13C 10B 9Be 1 0 6Li 7Li 6 7 8 9 11Be 12Be 8He 3He 4He 9Li 7B 13B 14B 15B 15C 16C 17C 10C 8Li 14C 9C 6Be 12B 9B 7Be 10Be 11C 6He 8B 5Li 10Li 11Li 14Be 1H 2D 3T n 0 1 2 3 4 5 N = No. of Neutrons

20. Chart of the Nuclei The Landscape ~300 stable ~ 7000 unstable … radioactive.

22. What makes a nucleus ‘stable’? • There is an ongoing interplay and competition between coulomb repulsion and strong nuclear force interactions • The result is that only certain combinations of Z and N give rise to stable configurations (about 300 in total). • Other non-stable types can ‘radioactively decay’ (about 7,000 predicted).

23. Radiation in our Environment We are all constantly subject to irradiation mainly from natural sources. There are three main sources of such radiation. • a) Primordial-around since the creation of the Earth ( 4.5 x 109years) • 235,8U ( and daughters including 210Po), 232Th or 40K (+ 87Rb, 138La and others....) • b) Cosmogenic – from interaction of Cosmic rays with Earth and atmosphere. • 14C, 7Be formed from cosmic ray interactions. Cosmic rays are mostly protons. • c) Produced or enhanced by human activity. • Medical or dental X-rays; • 137Cs (product from nuclear fission, 239Pu, • 241Am, 239Pu from weapons fallout

24. From NRPB-Average Radiation Dose in UK NRPB is now HPA-RPD

25. Radioactive species in the body Average amount by weight Activity Isotope U-Uranium 90μg 1.1Bq Th-Thorium 30 μg 0.11Bq 40K 17mg 4.4 kBq Ra 31pg 1.1Bq 14C 22ng 3.7kBq 3H-tritium 0.06pg 23Bq Po-Polonium 0.2pg 37Bq Some variation- for example smokers have 4-5 times more Po.

26. Z=43 Tc Z=61 Pm Z=84 Po Elemental composition of the Solar Nebula

27. How it all starts….Hydrogen (Z=1) to Helium (Z=2) The Proton-Proton Chain

30. Nuclear Fusion creates energy up to A~56 (Z=26 = Iron) If the star is hot enough, nuclear fusion will fuel the star and create elements up to A~56

31. Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page 33-38 Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209Bi...why?

32. Once you have 4He what next? • 4He + H→5Li not energetically allowed…neither is 4He+4He →8Be…we’re stuck with A=1,2,3 and 4…. • BUT!!! 4He can fuse with 2 other 4He (8Be) stuck together for a short time (~10-16sec) to make 12C…complicated but understood. • Once we have made 12C (Z=6) nuclei can fuse together and gain energy (if the star is hot and massive enough) to make all elements up to Z=26 (Iron=Fe).

33. DB ~1.5 MeV per A

35. Once you have 56Fe what next? • Top of the binding energy per nucleon curve reached at A~56…fusion above this costs energy…bad news for the star - supernova • BUT elements from 27-92 exist in nature – how are these made ? • Neutron Capture – neutrons have no charge – no electrostatic repulsion.

36. Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page 33-38 Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209Bi...why?

37. Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209Bi...why? Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page 33-38 Neutron capture… no electrostatic barrier to nuclear fusion…. all you need are enough Neutrons…

38. Beta –radioactive decay, (consequence of E=mc2) 2 types: (i) Beta- plus proton changes to a neutron (Z ->Z-1) (ii) Beta – minus neutron changes to a proton (Z -> Z+1)

39. Nuclear reactions in Red giant stars create ‘spare’ neutrons Stellar neutron sources in the middle of Red Giant stars (e.g., Betelguese) 13C+4He→17O*→16O + n 22Ne+4He →26Mg*→25Mg + n

40. So, how do you make Gold ? • Gold has 79 protons (i.e. Z=79) • Start with Z=78 protons (i.e. Platinum) • Specifically 196Pt ( Pt = Z=78, N=196-78=118) • Reaction is 196Pt + neutron to make 197Pt • 197Pt is radioactive and ‘beta-decays’ to make 197Au (i.e., normal ‘stable’ gold).

41. S-process makes 209Bi from 208Pb+n → 209Pb (T1/2=3.2hr) → 209Bi Neutron capture on stable 209Bi →210Bi (T1/2 =5 days) → 210Po. 210Po → a + 206Pb (stable nucleus, as is 207Pb and 208Pb) Polonium-210 ‘terminates’ the period table at Bi (via the s-process)

42. The Natural Decay Chain for 238U Qa(210Pb) = 5.41 MeV Ea = 5.30 MeV E(206Pb) = 0.11 MeV T1/2 = 138 days. ‘Radium’ ‘218At =Radium B’ 210Po =Radium ‘F’ Radon =‘Emanation’ C’ ‘218Po =Radium A’ E C D C’’ BUT: Evidently, heavier (radioactive) elements like Th (Z=90) ; U (Z=92) exist ? How are they made?

43. = 214Pb = 214Bi

44. SN1987a before and after !!

47. A=N+Z = fixed

48. Mass Parabolas and Radioactive Decays A = constant For a give fixed A (isobar), we have different combinations of Z and N. e.g., A=Z+N=137 can be from Z=56, N=81 →137Ba81 ; or Z=55, N=82 → 137Cs82 (see later)…

49. Example of a mass parabola 125Ba : Z=56; N=69 125In : Z=49 p → n + b+ + n n → p + b- + n A=N+Z=125 125Cs : Z=55; N=70 125Sn : Z=50; Mass energy (mc2) 125Xe : Z=54; N=71 125Sb : Z=51; 125I : Z=53; N=72 125Te : Z=52; N=73 STABLE ISOBAR FOR A=125

50. Figure Wiescher, Regan & Aprahamian, Physics World Feb. 2002, page 33-38 Slow-neutron capture process allows formation of elements from A~56 to A=209 (Bi)... terminates at 209Bi...why?